The present invention is directed to high-intensity discharge (HID) lamps and more particularly to an HID lamp with a starting aid.
HID lamps are started with a voltage that is higher than the operating voltage of the lamp and that provides an electric field sufficient to cause a breakdown, in the presence of an avalanche-initiating electron. Some starting aids use ultraviolet (UV) enhancers to assure the presence of the avalanche-initiating electron.
For example, U.S. Pat. No. 5,323,091 to Morris describes a UV starting aid for a metal halide arc discharge lamp that includes a cavity in a press seal of the arc tube, where the cavity includes part of the foil of the electrode seal. A ground plane is provided on the exterior of the press seal. The lamp is energized by charging the foil negative with respect to the ground. An electron leaks from a sharp edge of the foil and initiates a dielectric barrier discharge (DBD) in the cavity. The DBD produces UV and vacuum-UV (VUV) photons, depending on the fill gas and its pressure, which in order to facilitate ignition of the lamp have to reach the cathode in the main vessel. As the photons must travel through the press seal material their utility as a starting aid is diminished due to transmission losses
U.S. Pat. No. 6,201,348 to Nortrup et al. describes a starting aid for a metal halide discharge lamp in which an arc discharge tube is positioned inside a hermetically sealed jacket. The jacket contains a gas that aids in starting the discharge in the tube. An outer conductor extends on the outside of the jacket and is connected to one of the leads of the tube. When voltage is applied to the electrodes the presence of the external electrode concentrates the electric field near the adjacent internal electrode. This effect in itself helps the breakdown in the tube, but may also lead to formation of a DBD in the jacket. If the latter is the case then these photons must travel through the wall of the arc discharge tube and reach the cathode in the arc tube. Their effectiveness is greatly reduced because of lack of control over the location where the DBD may occur and its position with respect to the cathode. Additionally, the spectrum of the DBD photons depends strongly on the jacket fill gas and may be strongly absorbed by the gas before it reaches the cathode (typically N2, the DBD spectrum of which is shifted more toward visible light compared to Xe or Ar which contain strong UV and VUV components).
Butler et al. (U.S. Pat. No. 7,083,383) disclose a starting aid comprised of conducting strips embedded in the walls of the discharge space. Its primary purpose is to concentrate the electric field at the cathode to promote electron emission. Additionally, the aid can be viewed as a capacitively coupled external electrode and as such it may produce a DBD. This reference does not disclose formation of the photons or recognize the importance of the insulation and geometry in the production of the photons.
U.S. Pat. No. 7,187,131 to Budinger discloses a starting aid with two loops of wire round the neck of each of the electrodes, where the loops are connected and fed with an ignition pulse. The starting aid extends over the light-emitting part of the lamp, affecting the optical properties of the lamp.
Hon (U.S. Pat. No. 4,010,397) discloses an arrangement for triggering a flash lamp in which a conductive patch is bonded to a portion of the outer surface of the lamp and extended over a part of the high voltage electrode. This patent also does not recognize the importance of the insulation and geometry in formation of the photons.